1. Field of the Invention
The present invention relates to graphite electrodes and, in particular, to graphite electrodes incorporating stress relieving slots on or below the surface.
2. Description of Related Art
Carbon electrodes, particularly graphite electrodes, are used in such applications as electric arc steelmaking furnaces and other applications in which one end (usually the top) is physically and electrically connected to the furnace and power supply while the other, free end (usually the bottom) is consumed by the arc which is generated during operation to melt the metallic material in the furnace. The temperatures and thermal gradients are quite high in such an operation. As the electrode is being consumed, it is typically lowered into the furnace to maintain the desired gap with the molten metal. The electrode is thus subject to both thermal shock and physical vibration.
It has been found that large diameter graphite electrodes tend to suffer from deep axial splits in service, especially in high current dc furnaces. These cracks can grow and link up in use and lead to pieces of the electrode falling from the column. A discussion of the problems of cracking under thermal shock may be found in the article "Crack Propagation and Thermal Shock Damage in Graphite Discs Heated by Moving Electron Beam" by Shubert et al. (CARBON, vol. 24 no. 1, 1986 Pergamon Press Ltd.).
Efforts to date to overcome the problem of thermal shock crack propagation have generally dealt with attempting to improve the integrity of the carbon/graphite body and surface. However, these approaches do not fully overcome the aforementioned problem, and a long felt need exists to reduce the electrode failure rate due to thermal shock.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved carbon/graphite electrode which has improved resistance to thermal shock.
It is another object of the present invention to provide a method of making a carbon/graphite body which has increased resistance to crack propagation under extreme thermal shock conditions.
A further object of the invention is to provide a method of making such an improved carbon/graphite electrode which is cost effective.
It is yet another object of the present invention to provide such an improved graphite electrode for use in electric arc furnaces, such as those used in steelmaking.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.